1. Field
The present invention relates to equipment and methods for preparing samples for analysis. In particular, equipment and methods are provided for automated staining of biological samples on microscope slides.
2. Background
Many tissues do not retain enough color after processing to make their components visible under a bright-field microscope. Accordingly, it is common practice to add color and contrast to tissue components by staining the tissue with various reagents. In the past, the steps of staining a tissue sample for histological or cytological analysis were performed manually, a process that is inherently inconsistent. Inconsistent staining makes it difficult for a Histologist or other medical personnel to interpret slides and to make comparisons between different samples. Thus, a number of devices and methods have been described that serve to automate the staining process and reduce staining inconsistency. Labor costs and the burgeoning demand for anatomical pathology services also are driving the push for increased automation of the staining process.
Prior art devices for automated staining, especially for high volume staining with traditional reagents such as hematoxylin and eosin (H&E), are primarily of a “dip and dunk” type, where racks of slides are automatically lowered into and removed from a series of reagent baths. For example, U.S. Pat. No. 4,911,098 to Tabata describes an automated staining apparatus, where microscope slides holding tissue specimens are dipped sequentially into a large number of chemical solution containers. The slides are mounted vertically in a slide holder basket and a clamp that engages and disengages the basket is used to move the slides from solution to solution. The clamp can include a mechanism to tilt the basket, which aids in removing excess solution before the basket is submerged in the next solution. Additional automated staining devices of the “dip and dunk” type are described in U.S. Pat. No. 5,573,727 to Keefe, U.S. Pat. No. 6,080,363 to Takahasi et al., U.S. Pat. No. 6,436,348 to Ljungmann et al. and U.S. Patent Application Publication No. 2001/0019703, naming Thiem et al. as inventors.
A common shortcoming of the automated “dip and dunk” staining devices is the possibility for cross-contamination of samples that are simultaneously or sequentially introduced into the same solution baths. For example, cells that become dislodged from one slide can settle onto other slides introduced into the same bath. Another problem inherent to these designs is that as slide baskets are transferred from one bath to another, solutions used in later steps of the staining process become contaminated with residual amounts of solutions used earlier in the process. Furthermore, degradation (such as through oxidation) of solution components over time can lead to inconsistent staining unless the solutions are regularly replenished or exchanged, which is a time-consuming and wasteful process that typically disrupts work-flow in these “dip and dunk” type of automated stainers.
Another type of automatic staining apparatus delivers fresh reagents directly to individual slides. For example, U.S. Pat. No. 6,387,326 to Edwards et al. describes an apparatus for staining slides where slides are expelled one at a time from a slide storage device and individually treated at various staining stations as they move along a conveyor belt transport apparatus. Additional devices for automatically staining individual slides are described in U.S. Pat. No. 6,180,061 to Bogen et al., PCT Publication WO 03/045560, naming Tseung et al. as inventors, and U.S. patent application Publication No. US2004/0052685 naming Richards et al. as inventors. While such devices can successfully minimize cross-contamination of slides and help ensure that samples are consistently treated with fresh reagent, the individual treatment of slides lowers throughput. Therefore, the throughput of these individual slide staining devices can be problematic for use in primary staining applications (such as H&E staining) where the number of samples processed in a histology laboratory can run into the hundreds or even thousands per day.
What is needed, therefore, is an apparatus and method for consistent, high-throughput staining of microscope slides that also minimizes the potential for cross-contamination between slides. Furthermore, an apparatus and method that can be replenished with fresh reagents without interruption of work-flow is desirable.